1. Field of the Invention
The present invention relates to: a mobile communication method for transmitting a downlink burst from a base station to a mobile station by use of a frame structure including a first region and a second region; and a base station and a mobile station used in this method.
2. Description of the Related Art
In recent years, the “Worldwide Interoperability for Microwave Access (WiMAX) Forum” is promoting standardization of a mobile communication system including a WiMAX compatible mobile station SS and a WiMAX compatible base station BS.
In this mobile communication system, the WiMAX compatible base station BS transmits a downlink burst to the WiMAX compatible mobile station SS, by use of a frame structure including a MAP region (a first region) and a downlink burst region (a second region). FIG. 1, FIG. 2, and FIG. 3 show examples of the frame structure.
Specifically, the WiMAX compatible base station BS allocates: DL-MAP (allocation information of the downlink burst) and the like as transmission information in the MAP region; and a downlink burst concerning the DL-MAP and the like as transmission information in the downlink burst region.
Here, the DL-MAP includes information on a position in the downlink burst region where the downlink burst is allocated.
Meanwhile, as shown in FIG. 4, the WiMAX compatible base station BS transmits the transmission information in the downlink burst region (such as the downlink burst), to each WiMAX compatible mobile station with a directional beam by using an adaptive antenna system (AAS).
Here, the WiMAX compatible base station BS may also transmit part of the transmission information in the downlink burst region to all the WiMAX compatible mobile stations SS located in the area managed by the WiMAX compatible base station BS with a non-directional beam instead of using the AAS.
Moreover, the WiMAX compatible base station BS transmits the transmission information in the MAP region (such as the DL-MAP), to all the WiMAX compatible mobile stations SS located in the area managed by the WiMAX compatible base station BS with the non-directional beam instead of using the AAS.
However, in the above-described mobile communication system, there is a problem in that the WiMAX compatible mobile station SS cannot determine the position in the downlink burst region where the downlink burst is allocated, if the WiMAX compatible mobile station SS fails in reception processing of the DL-MAP transmitted from the WiMAX compatible base station BS, and therefore cannot receive the downlink burst.
In particular, as shown in FIG. 4, an area where the DL-MAP constituting the transmission information in the MAP region to be transmitted with the non-directional beam can be reached (such an area will be hereinafter referred to as a MAP region reachable area) is narrower than an area where the downlink burst constituting the transmission information in the downlink burst region to be transmitted with the directional beam can be reached (such an area will be hereinafter referred to as a downlink burst region eachable area). Accordingly, there is a problem in that a possibility of failure in the reception processing of the DL-MAP by the WiMAX compatible mobile station SS is higher than a possibility of failure in the reception processing of the downlink burst by the WiMAX compatible mobile station SS.
Moreover, in the above-described mobile communication system, a proportion of the DL-MAP in the frame structure becomes substantial by simply increasing the number of times for transmitting the DL-MAP in order to improve a reception probability for the DL-MAP. As a consequence, the transmission speed of the downlink burst is deteriorated.